Interview: Steve Threlfall, general manager, U-Battery

U-Battery’s general manager explains the thinking behind the latest generation of small modular reactors

Small modular reactors (SMRs) are a key part of the UK’s nuclear future. A competition is currently running — somewhat behind schedule — to pick a design to receive more funding and be taken forward to a first-of-a-kind demonstrator and future plants, to serve both the UK and, it is hoped, a large export market.

SMRs contradict the previous thinking behind nuclear reactors, which can be crudely summarised as ‘bigger is better’. This economy-of-scale thinking has been proved numerous times in many sectors – basically, it does not cost twice as much to build a plant with twice the capacity — but in nuclear it doesn’t seem to have worked. As time has gone on, nuclear reactors and their associated hardware have become increasingly complex, with more and more safety systems being added, with the result that they are so complex to build that even the most prosperous countries are strained to finance them.

The thinking behind SMRs is that another mechanism for reducing costs, mass production in factories – which has been proved across several sectors — will unlock savings. Break down a plant into modular systems that can be made in a central factory, construct and test those systems in these controllable surroundings, then assemble them on site, and the whole thing will be cheaper.

Most of the SMR designs competing in the UK and, indeed, being developed elsewhere are scaled-down versions of the pressurised water reactor (PWR) technology that has dominated the mainstream nuclear market for decades. An exception is U-Battery, a micro-modular reactor design, distinct from larger SMRs, promoted by a company formed by a consortium of nuclear and other engineering firms, including Amec, Cammell Laird, Laing O’Rourke and URENCO. U-Battery general manager Steve Threlfall recently met The Engineer to discuss progress on the design and explain how it was suited to a different range of applications from those of other reactors.

In some ways, the U-Battery system harks back to an earlier generation of reactors. Rather than being cooled by water, it is a high-temperature gas-cooled reactor (HTGR).

The U-Battery plant occupies about the same area as the penalty area on a football pitch

“We use Triso fuel,” Threlfall said. These are spherical pellets with fissile uranium, in an oxide form, at their core, surrounded by layers of carbon and silicon-based ceramic. “There are two things you can do with that. You can put it into tennis-ball sized spheres in something called a pebble-bed reactor, which was developed in South Africa; or you can do what we do, which is to use a prismatic block design.”

In this, he explained, Triso particles are embedded into pellets called compacts, 39mm x 26mm, which can be assembled into something like conventional nuclear fuel rods. These then go into the core, which is assembled from an array of 24 hexagonal graphite blocks 80cm high — the prismatic blocks of the name. These are pierced with holes that run axially up and down the reactor. Some of these holes contain fuel, some control rods, and others allow the coolant gas — helium — to circulate. Rather than boil water to create steam, the hot helium goes into a heat exchanger, warming a secondary coolant that expands, driving it around its circuit.

“It’s nitrogen in the secondary circuit, and that blows a standard turbine around,” Threlfall said. “We use nitrogen because it’s as close to air as you can get, which means we can use a standard off-the-shelf turbine. It helps keep the economics in good shape.

“There are very few actual nuclear components; it’s just those graphite blocks, the fuel itself, the pressure vessel and the heat exchanger. Everything else is standard equipment like you’d find in any conventional gas-fired power station. We keep it really simple.”

An advantage of this type of reactor is that all the fission breakdown products are kept
inside the Triso particle, which, unlike the fuel in an SMR, cannot melt if coolant in lost.

“If you take out the control rods and let the helium escape, the temperature will go up from the operating temperature, 700°C, to about 1,100°C — and the fuel is proven safe up to 1,600°C. The graphite expands, the neutrons escape and it shuts itself down,” Threlfall said. “Prof Tim Abram of Manchester University, who designed this type of reactor, has sat on a Triso reactor in China with the safety systems turned off with no ill effects.”

A long history
Triso, though not currently in use with commercial reactors, has a long history. “Triso fuel has been under test in the US for 13 years, and before that it was used in the UK at the Dragon reactor; it’s Technology Readiness Level 9,” Threlfall said. “It’s performed way better than anything we’d need.”

Triso is not currently used because it is best suited to co-generation of heat and power, rather than the pure power generation for which SMRs are optimised, which has been the dominant paradigm for using nuclear. Now that the use of fossil fuels for heating is receiving more scrutiny, U-Battery believes that Triso, which can provide both heat and power with no carbon emissions, is a technology whose time has come.

“It hasn’t been done before because we’re trying to address this different market where nuclear hasn’t been before,” Threlfall said.

Although U-Battery is in the UK’s SMR competition, it has an eye on other markets: two in particular. “There’s interest in the UK, Canada and Poland. Ideally we’d like to do all three simultaneously but things work at different speeds.”

In Canada, Threlfall explained, U-Battery units could serve more than 300 remote communities, many of which are involved in mining and based around the Hudson Bay and Arctic Circle. “Today they run diesel generators; they’re dirty, not so reliable and incredibly expensive to run because of the cost of getting diesel to these places on ice roads or by air.” A single-reactor U-Battery plant, providing 10MW of heat and up to 4MW of electricity, would be ideal for communities of around 2,000 people, Threlfall said.

The situation in Poland is slightly different. “There is a great interest in Poland to replace boilers on existing industrial sites with a nuclear heat source; to replace coal or gas from Russia and improve their energy independence.”

The design for U-Battery has yet to reach a working prototype, Threlfall admits. “Over the past 12 months industrial partners conducted a two-stage detailed study of the costs including fuel, construction, licensing, training and commissioning costs,” he said. This yielded some pleasant surprises.

“We went initially to Sheffield Forgemasters for the pressure vessel and they said: ‘Actually, it’s so thin and small that you wouldn’t really want to forge it; you’re much better off fabricating it.’ So we went to Outokumpu in Sheffield and they did some costings for a welded pressure vessel in a nuclear-grade steel – so much cheaper than forging.”

The company now needs to expand its design team for front-end design and intends to go straight to building a first-in-class plant rather than prototyping.

Because of the simplicity of the U-Battery reactor, Threlfall believes it could be in operation before any SMR-based designs, even in the UK, where other partners in the company are bringing their expertise to the task.

“We’re aiming for a mid-2020s start-up for our first-of-a-kind plant,” he said. “And we’ve also had interest from India.”

The Chinese are and so should we, but for some reason our decision makers seem to have adopted a “not invented here” attitude. The liquid salt systems developed by the USA at Oak Ridge were small and demonstrated the advantages of a system intrinsically safe, with very low nuclear waste production. Google Kirk Sorensen for more information.

This system is still enclosed in thick concrete shielding and steel pressure vessels. The fuel elements themselves are enclosed in a hard ceramic shell. It would take a small nuclear weapon to breach all the containment.
The ceramic fuel elements would also tend not to disperse and will contain the fission products, Sr90, I131, etc which tend to spread after a nuclear accident/explosion.

I believe that the gas cooled reactors have much less need of a pressure vessel – and that there could be ways of making them as layered lightweighted metal structures – possibly using carbon fibre too (as some oxygen tanks do). And the use of a gas rather than water means there is no potential catastrophic phase change and very high pressures.
Plus, I believe, helium might not have radioactive isotopes.
This makes for a simpler system – from a safety point of view. (Though I appreciate there are other requirements such as corrosion & refuelling to be considered).
I am not sure I understand why this reactor is for process heat and domestic power (as the Magnox & AGRs were not); is it something to do with ancilliary plant (turbines etc…)?

I welcome any developments in advancing the use of nuclear energy, however I find this article lacking in depth and to represent misinformation on SMR. The Chinese Generation IV 2 × 250 MW th HTR-PM demonstration Reactor has already received it TRISCO fuel, and commercial operation is scheduled for the end of 2017. The Chinese completed their TRISO fuel-production factory in Baotou, Inner Mongolia, and trial production began at the plant in 2015. The Chinese have with their HTR-10 10 MWt prototype pebble bed reactor accumulated some 17 years of experience. TRISO fuel particles were originally developed in the United Kingdom as part of the Dragon reactor project. The inclusion of the SiC as diffusion barrier was first suggested by D. T. Livey. The first nuclear reactor to use TRISO fuels was the Dragon reactor and the first powerplant was the Japanese THTR-300 a helium-cooled high-temperature reactor with a pebble bed core consisting of approximately 670,000 spherical fuel compacts each 6 centimetres (2.4 in) in diameter with particles of uranium-235 and thorium-232 fuel embedded in a graphite matrix.

There is a perfectly viable way to clean up diesel IC, but the powers that be apparently are not listening. Hyrogen generated using the ACE cell makes a remarkably pure H2 stream, and this entrained in the air intake speeds up flame velocity during the power stroke, resulting in far less unburned fuel, and about 30% savings on fuel consumption for the same power, all without proportional mass of hydrogen in lieu of diesel. It only takes a small percentage of the mass flow to accomplish wonders.

It also exists since years ago the CAREM , an ultra-safe SMR developped by INVAP SE from Argentina, to manufacture radioisotopes and supply 25Mwe power+ 100Mw thermal.
Can be studied here: http://www.invap.com.ar

Given the shambles in the PWR designs available to us, it may be worthwhile building another AGR, copying hartlepools, Torness or Heysham say. We could even build some of the machinery if we invested in UK industry for the future instead of importing everything as with the PWR designs.

The SMR should obviously be developed to the prototype stage as a minimum as part of the UK keeping some high technology outside of armaments, food and pharma.

The U-Renco Ubattery is not new, the have been working on this design for some time and offers a design that is safe (black world -no support safety power needed. If as a country wanting to step up in the world and hopefully free from EU prevarication we should consider district heating (not new concept) and local power on a truly interconnected power grid. In the 1950s and ’60s we had local coal fired power stations which due to thermal efficiency and fuel management was a major drawback, this type of reactor could provide with larger base load units a truly magnificent step towards cleaner energy manufacture and management. Good luck U-Battery

” NIMBY” “Can’t fail but Murphy’s law – will fail technology” “GIGO” and therefore reconsider your assumptions ! Much better solutions available – lower risk & higher longer paybacks – without China Syndrome
All you folks can have one these micro reactors in YOUR backyard- ill pass on that. Hoping there are plenty more people like me who are still sane. Thank you.